This application is a 371 of International Patent Application No. PCT/NO01/00005 filed Jan. 15, 2001, now WO 01/50052 A1 published Jul. 12, 2001, and claims priority benefits of Norwegian Patent Application No. 2000 0058 filed Jan. 6, 2000.
The invention relates to a pressure regulating valve for controlling an upstream fluid pressure in relation to a reference pressure by regulating the fluid quantity let through the valve, comprising a housing having an upstream inlet and a downstream outlet for the fluid, a pressure-sensitive element for sensing the pressure difference between the upstream pressure and the reference pressure, and a spring-loaded regulating piston which, in cooperation with a seat, is arranged to regulate a flow passage between the inlet and the outlet, the piston being operatively connected to the pressure-sensitive element, to change its position in relation to the seat in accordance with the position of the pressure-sensitive element.
The regulating valve according to the invention has been developed in order to be able to maintain a defied pressure difference between an upstream fluid and another fluid having an unstable pressure. It is especially developed for the purpose of being able to maintain an accurate pressure difference between two fluids flowing in separate courses in gas-diffusing diaphragms, such diaphragms being very expensive and not able to tolerate that said pressure difference exceeds given values. Considered generally, the invention is applicable in most situations where it is important to maintain an accurate pressure difference between fluids, or keep a constant pressure of a fluid relative to a given reference pressure.
A relevant field of use for the pressure regulating valve according to the invention is to control the pressure difference across gas-diffusing diaphragms used for removing CO2 from natural gas. For the sake of simplicity, the following description takes its starting point in such an application. It is here natural to let the natural gas represent the reference pressure, the fluid controlled by the pressure regulating valve preferably being a liquid (for example amine) having a great ability of absorbing CO2.
For achieving an optimum diffusion speed, one has to adapt the dimensions of the gas-diffusing diaphragm to the flow velocity of the natural gas and the CO2absorbing liquid, respectively. The flow velocity of the liquid preferably is controlled by a pump, care being taken, by means of a pressure regulating valve according to the invention, that the liquid, when passing through the gas-diffusing diaphragm, has a desired pressure relative to the natural gas. Preferably, this is done by arranging a throttling on the liquid line upstream of the gas-diffusing diaphragm, and by arranging a pressure regulating valve according to the invention downstream of this diaphragm, to control the flow resistance so that the liquid pressure at any time has a desired value.
Generally, it will be natural to see to it that a desired liquid pressure is established in the region between a pressure regulating valve and a throttling, the regulator controlling the through-flow of the fluid so that a desired pressure level is achieved in this region. In principle, one may choose to arrange a pressure regulating valve upstream of said throttling. In that case the pressure regulating valve must he arranged to regulate the downstream pressure to a desired value.
The pressure of the natural gas typically may have a magnitude of 70-100 bar. Gas-diffusing diaphragms can stand a high total pressure, but might be damaged if the pressure difference between the natural gas and the amine exceeds e.g. 0,7 bar. In order to optimize diffusion, it is desirable that a certain pressure difference between the two fluids is established. Consequently, it is very important that such a pressure regulating in valve functions optimally.
In the market there exist many types of regulators which are constructed to carry out corresponding regulating functions. The general designation of these regulators is back pressure regulators. However, none of the regulators of which one knows, have been able to exhibit the desired properties with respect to giving a stable and smooth pressure regulation, at the same time as they manage to correct sufficiently rapidly on deviations, so that one avoids pressure pulses which might damage the expensive gas-diffusing diaphragms.
The regulating function of a pressure regulator will always to a certain extent be influenced by pressure and flow variations, since such variations change the force that must be generated to correct for deviations.
On this background the object of the invention is to provide a pressure regulating valve which is without the above-mentioned drawbacks, the valve giving a stable and smooth pressure regulation at the same time as it manages to correct sufficiently rapidly on deviations, so that harmful pressure pulses are avoided, and wherein pressure and flow variations have a particularly small influence on the regulating function.
For achieving the above-mentioned object there is provided a pressure regulating valve of the introductorily stated type which, according to the invention, is characterized in that the regulating piston is slidably arranged on the outside of a guide sleeve having openings for flow of liquid from the flow passage to the outlet, and that the valve comprises a chamber defined between an end surface of the guide sleeve and an inner end surface of the piston, and a pilot body which is mechanically coupled to the pressure-sensitive element and is arranged to open ducts for supply of fluid from the inlet to the chamber or delivery of fluid from the chamber to the outlet dependent on the position of the pilot body relative to the regulating piston, so that the piston changes its position dependent on the chamber volume and thereby in accurate correspondence with the position of the pressure-sensitive element.